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annotate planemo/lib/python3.7/site-packages/networkx/generators/cographs.py @ 1:56ad4e20f292 draft

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"planemo upload commit 6eee67778febed82ddd413c3ca40b3183a3898f1"
author guerler
date Fri, 31 Jul 2020 00:32:28 -0400
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1 # -*- coding: utf-8 -*-
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2 # Copyright (C) 2004-2019 by
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3 # Aric Hagberg <hagberg@lanl.gov>
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4 # Dan Schult <dschult@colgate.edu>
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5 # Pieter Swart <swart@lanl.gov>
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6 # All rights reserved.
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7 # BSD license.
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8 #
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9 # Authors: Efraim Rodrigues (efraimnaassom@gmail.com)
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10 r"""Generators for cographs
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11
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12 A cograph is a graph containing no path on four vertices.
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13 Cographs or $P_4$-free graphs can be obtained from a single vertex
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14 by disjoint union and complementation operations.
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15
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16 References
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17 ----------
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18 .. [0] D.G. Corneil, H. Lerchs, L.Stewart Burlingham,
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19 "Complement reducible graphs",
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20 Discrete Applied Mathematics, Volume 3, Issue 3, 1981, Pages 163-174,
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21 ISSN 0166-218X.
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22 """
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23 import networkx as nx
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24 from networkx.utils import py_random_state
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25
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26 __all__ = ['random_cograph']
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27
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28
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29 @py_random_state(1)
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30 def random_cograph(n, seed=None):
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31 r"""Returns a random cograph with $2 ^ n$ nodes.
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32
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33 A cograph is a graph containing no path on four vertices.
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34 Cographs or $P_4$-free graphs can be obtained from a single vertex
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35 by disjoint union and complementation operations.
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36
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37 This generator starts off from a single vertex and performes disjoint
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38 union and full join operations on itself.
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39 The decision on which operation will take place is random.
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40
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41 Parameters
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42 ----------
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43 n : int
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44 The order of the cograph.
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45 seed : integer, random_state, or None (default)
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46 Indicator of random number generation state.
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47 See :ref:`Randomness<randomness>`.
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48
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49 Returns
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50 -------
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51 G : A random graph containing no path on four vertices.
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52
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53 See Also
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54 --------
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55 full_join
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56 union
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57
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58 References
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59 ----------
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60 .. [1] D.G. Corneil, H. Lerchs, L.Stewart Burlingham,
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61 "Complement reducible graphs",
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62 Discrete Applied Mathematics, Volume 3, Issue 3, 1981, Pages 163-174,
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63 ISSN 0166-218X.
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64 """
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65 R = nx.empty_graph(1)
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66
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67 for i in range(n):
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68 RR = nx.relabel_nodes(R.copy(), lambda x: x + len(R))
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69
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70 if seed.randint(0, 1) == 0:
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71 R = nx.full_join(R, RR)
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72 else:
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73 R = nx.disjoint_union(R, RR)
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74
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75 return R